The climate warmed after the ice age of the Late
Carboniferous and earliest
Permian, and a rich flora evolved that
was characterised by Glossopteris. Coal deposits were
formed in extensive areas of cool-temperate swamps where plant
communities thrived. For the first time Ginkgoes and Conifers make their
appearance in the fossil record, colonising the drier hill sides, not
requiring swamps for their survival. There were also many tree ferns.

As the continental ice sheets melted in the earliest
Permian
the rising sea inundated large areas of Australia. The southern part of
the continent was the first to become dry land again when the seas
retreated. In Western Australia the
Canning
and
Carnarvon Basins and in Queensland the
Bowen Basin
remained flooded by the shallow seas until the Middle Permian.

As a result of folding and uplift in the New England region, the areas
covered by the sea around the margins of the continent was reduced, on
the east coast the remaining continental sea covered an area between
Rockhampton in Queensland and Grafton in New South Wales.

Though the climate was gradually warming, the
Permian was still a cold
time, the higher areas still being covered with alpine glaciers,
especially on the mountains in the southeast of the continent. Much of
this mountainous country had risen during the Kanimblan Orogeny of the
Carboniferous. During this orogeny, a wide belt extending from Tasmania
to Cape York underwent a period of uplift and deformation. It was the
most severe orogenic event known to affect the Tasman Geosyncline.
Ice-rafted boulders and drop stones are present in sediment deposited in
the Sydney Basin during the Permian, evidence that the area was still
subject to freezing winters. Trees petrified in this period give further
evidence of a strongly seasonal climate in the growth rings in their
wood.

At this time the climate in the northern part of the continent,
Queensland, Western Australia and the Top End of the Northern Territory,
was warmer than that in the south of the continent, and strongly
seasonal, the summers are believed to have been temperate. Especially in
the half of the continent, large areas of the drainage basins were
occupied by coal swamps, smaller ones occurring in Western Australia and
South Australia.

As the seas retreated after the transgression in the North-West Shelf
area of Western Australia in the
Triassic deltas formed. The accumulated
sediments incorporated the gas reservoirs of the area. The main origin
of the gas was from plant remains in the the deltas, but also from the
marine organic matter.

There was a great expansion of plant life as the climate was warming,
the floral remnants that survived the ice age gave rise to the
Glossopteris Flora. The coal swamps of the Australia Permian
were not the steamy tropical swamp-jungles of the Northern Hemisphere,
being cold swampy bogs where Horsetails flourished like rushes. A dense,
low swamp vegetation composed of ferns, Seed-ferns, and possibly mosses
like peat, herbaceous Lycopods, such as Selaginella, grew
in dense masses. In the swamps and adjacent areas of high water table,
trees, shrubs and Glossopteris grew that had specially
adapted aeration roots to allow them to grow in boggy conditions.
Mangroves use the same type of roots to grow along the coasts at
present.

The Glossopterids were deciduous, because of the very cold winters, and
the Ginkgos were probably also deciduous. Those plants that retained
their leaves would have spent the winter in a dormant state.

The Glossopterids

Glossopterid leaves are common and widespread in the
deposits from the Permian of the southern continents that were part of
Gondwana. They are also the most difficult to classify, because of the
great diversity of venation patterns and the problems of assigning
leaves on morphology alone.

Some of the leaves had a midrib and a network of secondary veins similar
to those of dicotyledons by the end of the Permian, and Parallel veins
are found in some as in Monocotyledons and some conifers. as in
Bennettitalean Cycads, some taenopteroid, and some were very small and
are believed to possibly be from plants that were woody herbs. In this
Order of plants all leaf types were present, the Glossopterid
Flora had the genetic potential to evolve in many directions. Some
may have been the base of direct lines leading to living plant groups.

In the Glossopterids, an essential character of the leaves is the
presence of lateral veins connected by cross connections, that resulted
in a mesh or net-venation pattern on the leaf lamina. If there is a
midrib the leaf is classified as Glossopterids. If there
is no midrib, but there is a median groove and there is also a mesh
pattern on the lamina like that in Glossopteris, it is
assigned to the form-genus Gangamopteris. If there is no
midrib and few cross-connections between the lamina veins, it is assigned
to Palaeovittaria.

The midrib of Glossopteris is not a single vein, but is
composed of a number of a number of veins that appear to be a single
strand when they are close together, but they can be clearly seen when
they are spaced more widely. Leaves are often grooved along the median
line, some having a keel of thickened tissue for extra support. From
leaves with a clearly defined midrib (Glossopteris), there
is a gradation to types with well spaced strands that aren't aggregated
into a midrib (Gangamopteris). If the preservation of the
leaf is not good it can be difficult to decide if there is a midrib or a
median groove. Leaves classified as Gangamopteris also
grade to the leaf type at the other extreme, Palaeovittaria.

All the known leaf form-genera of Glossopterids have similar
fructifications, so they are classified into a single order. As more
complete plants can be reconstructed from the fragmentary evidence they
are given a more detailed scientific classification.

As with eucalypts today, the Glossopterids dominated the
vegetation of the entire landmass of Gondwana, They were an order of
plants, and the similarity of their leaves , as well as their
classification into genera, such as Glossopteris, is
misleading. Eucalyptus is a genus with 450 species (it may
possibly be reclassified as several closely related genera). Among the
genera of the Myrtaceae, the family to which Eucalypts belong, some have
similar leaves but different floral structure. Their classification is
scientific because the structure of all their floral structures is
known, so there is no need for subjective judgment when classifying
them.

Glossopterid leaves are rarely found attached to a stem. Nearly all
leaves in some shale deposits are the result of the trees being
deciduous, leading to the accumulation of "autumnal banks" in lakes and
estuaries during autumn. Glossopterid leaves come in a wide range of
sizes, from those of Glossopteris ampla, with leaves up to
1 m long and of almost a similar width, to very small leaves, with all
sizes between the extremes. The leaf shape varies from short, wide
leaves to long, narrow leaves, and the apices of the leaves could be
indented, pointed or blunt. The blade of some leaves tapered towards the
stem, others bulged out into a heart-shaped base. The leaves in forms
like Glossopteris duocaudata were shaped like a swallow
tail. The petioles (leaf stalk) could be long, short or missing. The
venation varied from fine, regular meshes to larger meshes at the midrib
or large meshes covering the whole leaf blade. There was also variation
of the angle between the lateral veins and the midrib and margin.
Occasionally small branches are found that show that the leaves were
attached in whorls or close spirals on the ends of small branches, the
scar pattern visible on the branches indication where leaves had been
attached in previous growing seasons.

Glossopterids were woody plants growing to the size of trees, and
probably shrubs, that were presumable adapted to grow in the different
habitats available at the time. They had Araucarioxylon
typy wood ( a gymnospermous wood with tracheids of regular size).

The root systems were adapted for growing in swamps, having a
specialised internal structure that is believed to have assisted in
aeration. These roots are called Vertebraria, as their
segmented cores resemble a vertebral column. Specimens of
Vertebraria have been found that have the point at which they
joined the trunk, showing the transition from the structure of the root
to that of the trunk. The other end of Glossopterid trees are also
known, the ends of smaller branches with attached leaves. An overall
picture of the plant is now known, giving some idea of what they looked
like in life. The structure of the shrubby forms and woody herbs can
only be guessed at, but they must have been present by the Late Permian,
and they probably didn't look much different from the equivalent sorts
of plants living at the present.

The earliest known Glossopterid leaves, Glossopteris
cyclopteroides and Gangamopteris angustifolia are
found in the glacigene sedimentary rocks at Bacchus Marsh, Victoria.
These deposits resulted from glacier activity during the Late
Carboniferous and Early
Permian ice age. The first Glossopterids known
from the Sydney Basin are found in the Dalwood Group, Lochinvar
Formation, Lower Marine Series, form the Early Permian.

The origin of the Glossopterids is very uncertain, but a possible
ancestral plant has been proposed, an aphlebiate plant from the
Carboniferous that lost the pinnate phase of its leaves.

Glossopterid reproduction

The similarity of leaves doesn't appear to indicate a similarity of
reproductive structures among the Glossopterids.

Female Reproductive Structures in Glossopterids

These are significant in the evolution of later plants from later
periods. The different types of Glossopterid fruiting bodies that have
been found characterise several plant groups in the Mesozoic, the
origins of which are believed to probably be in the Glossopterid gene
pool.

There are 2 distinct types of female reproductive structures among the
Glossopterids, and they are different enough to divide the Glossopterids
into 2 separate groups. One section has massive "fruits" containing many
seeds and are carried on unmodified leaves. Within this group, the
evolutionary sequence leads from a condition with fruits having many
seeds to fewer seeds and also a trend towards the fusion of the bract
(cover leaf), part of the fruit, with the receptacle containing the
seeds. For the purpose of inclusion in a new classification, a suggested
designation Glossopteridales, Sect. Megafructi.

The other Section, in which the seeds are attached to modified leaves or
scale-leaves. Classification of this Section then becomes
Glossopteridales, Sect. Microfructi. A similar situation exists
in male reproductive structures that are known to belong to
Glossopterids, the sporangia being borne of modified leaves or
scale-leaves.

Section Megafructi

The first attached reproductive structures, from South Africa, are all
from this section. Many specimens have now been found in India and
Australia, allowing the structure of some of the different types to be
understood in more detail, making it possible to make reconstructions.

All the reproductive structures of this type are borne on normal leaves,
being either stalked or sessile, attached to the petiole or to the leaf
blade at any point along the midrib. The distinguishing of a number of
genera has been enabled by where they are attached. It has been found
that some names given before enough knowledge had accumulates were
premature, being given to fossils that were deformed by the process of
fossilisation, and even to the state of maturity of the structure,
instead of diagnostic features.

It appears the basic arrangement may be fruit composed of a
receptacle (core), seeds being attached all around it, and protected by
a bract (cover-leaf) while it is developing, thought to have fallen off
when the fruit is ripe. The receptacle was either spherical or
cylindrical (or of oval cross-section by dorso-ventrally flattening).

There are several lines of evolution arising from the basic fruit with
the seeds attached all around the receptacle and a cover leaf. Some
lines involve fusion of the fruit parts, either with each other or with
the foliage leaf they are borne on. Some have reduced seed numbers,
still others show a combination of both trends.

The fruit, are either stalked or sessile, attached to the leaf base or the
petiole of the foliage leaf, in Plumsteadia, Scutum
and Dictyopteridium. Seeds can be wingless (or with a
surrounding narrow wing), or have a pronounced wing (Indocarpus
type). Plumsteadia and Dictyopteridium have
the former type, while Scutum has the latter, with an
appearance of a fluted ring around the compressed fruit.

Specimens described as "Lanceolatus, from South Africa,
have sessile fruit attached further up the leaf, and possibly fused to
it, especially in the younger stages. When specimens in the Plumstead
collection where examined in Johannesburg, the state of preservation
wasn't good enough to determine if the cover-leaf was fused to the
seed-bearing organ. The fruit has uniform rounded seeds, but the
receptacle is much flatter and probably unifacial, appearing to be of
the same general type as Plumsteadia.

In Australia, a fertile structure that takes the fusion to a later
stage, described as Senotheca, appearing to consist of
2 rows of seeds attached to the midrib edges. Jambadostrobus
and Venustotrobus are 2 genera from India. The former has
a Plumsteadia-type fruit in which 2 or 3 seeds attached to
the midrib in the mid region of the lamina. In the latter, a
Scutum-type fruit has a wing and a cover leaf that is attached in
the middle of the leaf.

Another form of fruit from India, from where the genus was originally
described, described as "Ottokaria", has a long stem, and
the head appears to be flattened, with a prominent wing and a coverleaf.
This fruit is of the Plumsteadia-type, the coverleaf has
become a wrap-around structure. It is the Indian specimens and
reconstructions that define the genus.

Austroglossa is a form in which the seed number has been
reduced in the Megafucti. The fruit has become a small number of
Nummulospermum type, platyspermic seeds, that attach to a small
branch attached to the petiole of a Glossopteris leaf.

A few specimens display the final stage of seed reduction, the single
large Samaropsis-type seed with a narrow wing being
attached to the base of a Glossopteris leaf. They are a
larger version of the seeds seen in Plumsteadia. Similar
large seeds have been described in South Africa, in which the seeds are
attached directly to the midrib of Glossopteris leaves.
This arrangement is the final stage of seed reduction that began with Jambadostrobus fruit.